Refrigeration system having improved heat transfer and reduced power requirements

ABSTRACT

A refrigeration system employing oil-lubricated compressors has an improved arrangement for removing oil from the refrigerant, and by use of a liquid pump and with utilization of by-product heat from the compressed gas, is enabled to operate with reduced power consumption. In addition, oil-removing apparatus adapted for installation in conventional refrigeration systems, and an improved defrosting arrangement utilizing oil-free gas, are disclosed.

United States Patent 1 Miller 1 Sept. 24, 1974 REFRIGERATION SYSTEM HAVING IMPROVED HEAT TRANSFER AND REDUCED POWER REQUIREMENTS [75] Inventor: Bruce D. Miller, Louisville, Ky. [73] Assignee: Refco, Inc., Jeffersontown, Ky.

[22] Filed: Oct. 9, 1973 [21] Appl. No.: 404,224

[52] U.S. Cl 62/192, 62/84, 62/81, 62/151, 62/277, 62/470, 62/471, 62/473, 62/509 [51] Int. Cl. F25b 31/00 [58] Field of Search 62/81, 84, 192, 194, 151, 62/277, 470, 471, 473, 509

[56] References Cited UNITED STATES PATENTS 320,307 6/1885 Suckert 62/84 1,500,280 7/1924 Shipley 62/473 1,944,472 1/1934 Sloan 62/471 2,097,725 11/1937 Gay 62/192 2,729,950 l/l956 Toothman 62/277 2,763,131 9/ 1 956 Sorensen 2,983,112 5/1961 Batteiger 3,021,689 2/1962 Mieler 3,534,564 10/1970 Mieler 62/470 Primary Examiner-William .l. Wye Attorney, Agent, or Firm-William E. Sherwood [5 7 ABSTRACT A refrigeration system employing oil-lubricated compressors has an improved arrangement for removing oil from the refrigerant, and by use of a liquid pump and with utilization of by-product heat from the compressed gas, is enabled to operate with reduced power consumption.

In addition, oil-removing apparatus adapted for installation in conventional refrigeration systems, and

an improved defrosting arrangement utilizing oil-free gas, are disclosed.

23 Claims, 10 Drawing Figures REFRIGERATION SYSTEM HAVING IMPROVED HEAT TRANSFER AND REDUCED POWER REQUIREMENTS BACKGROUND OF THE INVENTION The necessity for removing oil from refrigerant in order to operate a refrigeration system at optimum efficiency has long been recognized, and many proposals to serve this purpose including my earlier US. Pat. No. 3,534,564 have been advanced. Oil-lubricated pumps, fans, or compressors driven by power consuming motors are a conventional part of a commercial refrigeration system and are the source of the oil found in the refrigerant. Accumulation of such oil over a period of time adversely affects the heat exchange within the system thus indicating the need to remove oil periodically. Furthermore, after oil is separated from refrigerant and collected, the continued operation of the system prior to removal of the oil may cause some of the collected oil to go back into suspension due to surge flow, or to pressure changes, or to violent agitation of flowing liouid refrigerant in contact with a quiescent body of collected oil.

Moreover, when plant pressure of the system is determined by the condenser pressure found in a single receiver and has to be sufficient to force the refrigerant through the expansion valves, it follows that the compressor must supply the hot gas to the condenser at a high pressure and that the motor driving such compressor uses more power than if such gas pressure were lower. In addition, if part of the heat in the hot gas leaving the compressor can be employed to attain a plant pressure which is greater than the condenser pressure, then less power also would be needed.

In recognition of these factors it is a purpose of the present invention to make available an improved system with reduced power requirements and with an optimum heat transfer which is due primarily to the relatively oil-free nature of the refrigerant.

SUMMARY The refrigeration system of the invention includes the usual condenser, evaporator and compressors, together with first and second receivers operating respectively at condenser pressure and at plant pressure, and with a vaporizer which serves simultaneously to pre-cool gas passing from the compressor to the condenser and to provide a cushion of gas in the second receiver at plant pressure. At least one means for collecting oil during desuperheating of compressed gas and for removing the collected oil from the system is employed in order to improve the heat transfer within the system.

Among the objects of the invention are the provision of an improved refrigeration system characterized by its efficient heat transfer and its reduced power requirements; the provision ofa system having a desuperheater and oil separation unit interposed between the compressor and condenser and having gas and liquid contact between hot gas supplied from the compressor and liquid supplied from the condenser; the provision of a system having vaporizing means containing a heat storage liquid and serving jointly to precool compressed gas passing to a condenser; to flash refrigerant liquid and to provide a cushion of gas under pressure on a receiver, and to employ the storage liquid for rapid vaporization in response to pressure changes in the system; the provision of a system wherein the evaporator may be defrosted by supplying an oil-free refrigerant gas thereto; the provision of a system including a receiver into which liquid is introduced through a distributor which minimizes agitation at the bottom of the receiver and is withdrawn by an outlet pipe whose end is enclosed within a trap which reduces agitation at the bottom of the receiver; the provision of a system having a pump for transferring liquid refrigerant from a first receiver to a second receiver and with the intake of the pump being connected to a suction tank filled with liquid from the first receiver and maintained in subcooled condition to prevent flashing at the pump entrance; the provision of a system having an oil trap automatically draining collected oil from the system in response to operation of a thermostatically controlled valve; the provision of a system including a condenser to which the cooling medium for condensing is supplied in response to the condenser pressure established in a first receiver and which inhibits boiling of liquid in the receiver and foaming of oil entrapped in the receiver as the system pressure varies; and the provision of means of the above-mentioned nature which may be added to existing refrigeration systems in order to improve the efficiency of the same and without requiring complete reconstruction of such existing systems.

These and other objects and advantages of the invention will become more apparent as the description proceeds and when considered in conjunction with the accompanying drawings in which FIG. 1A is a diagrammatic view of one portion of a preferred refrigeration system embodying the invention. a

FIG. 1B is a similar view of the remainder of the system complementary to the showing of FIG. 1A.

FIG. 2 is a view of the improved oil removing trap shown in conjunction with a desuperheater.

FIG. 3 is a side elevation view of the improved combined desuperheating and oil separating vessel with interior structure indicated by dotted lines.

FIG. 4 is a view taken on line 44 of FIG. 3 and showing the control of liquid supply to the vessel.

FIG. 5 is a view to a larger scale of the vaporizer with parts shown in section.

FIG. 6 is a transverse sectional view of a receiver showing the liquid distributor in elevation.

FIG. 7 is a plan view of a portion of a receiver showing the location of a box trap therein.

FIG. 8 is a transverse sectional view of the receiver on line 8-8 of FIG. 7 and showing the box trap in position, and

FIG. 9 is a side elevation view of the box trap.

Referring first to FIG. IA, cold spent gas from the evaporator is supplied through pipe 10 to an oillubricated booster compressor 11 and delivered therefrom into a desuperheater vessel 12 through pipe 13. For purposes of illustration and not oflimitation and in order to define more clearly the efficiency of the present system, certain representative values of temperature and pressure are given for an ammonia system, and for example the gas in pipe 10 may be at about 20F. at a pressure of about 1 p.s.i.g. and the gas entering the vessel 12 may be at about 200F. and at a pressure of about 30-40 p.s.i.g. At the lower portion of this vessel a pool of liquid refrigerant is maintained as later to be described and oil contained in that poolis removed from the system by an improved oil-collecting and removal trap attached to the vessel as will later appear.

The desuperheater provides a gas and liquid contact since pipe 13 delivers the compressed gas to a point below the surface of the pool and as a result of this contact gas leaving the upper portion of the vessel through pipe 14 may have a temperature of only about 30F. Conventional apertured baffles 15 within the vessel serve to remove liquid from the rising gas in the vessel.

A main oil-lubricated compressor (which like the compressor 11 is driven by motors not shown) receives gas from pipe 14 and delivers it by pipe 21 through a vaporizer generally shown at 22, the purpose of which will later appear, and to an improved desuperheater and oil-separating unit generally shown at 23. The oilcontaminated gas entering this unit at about 200F. and at a pressure of about 76 p.s.i.g. is cleansed therein and leaves the unit through pipe 24 at a temperature of about 75F. and at its entering pressure, approximately.

Pipe 24 delivers the clean gas through pipe 25 into an elevated condenser generally indicated at 26 and a defrosting branch pipe 27 and an equalizing branch pipe 28 also communicate with pipe 24. Refrigerant liquid leaving the condenser through pipe 30 is delivered to a first receiver 31 equipped with improved means for avoiding carryover of oil which may settle in the receiver. Equalizing pipe 28 connects with the gas space of the receiver and is equipped with a check valve 32 opening in the direction of unit 23. Refrigerant liquid is delivered from the first receiver at the condenser pressure, which may be about 75 p.s.i.g., to an upper portion of a suction tank 33 by means of pipe 34 and normally will completely fill such tank. To prevent flashing of the liquid in the tank a cooling coil 35 is disposed therein and refrigerant liquid containing oil, and supplied through pipe 36 from a trap 37 attached to the lower portion of Unit 23 is connected to the lower end of this cooling coil. From the upper end of coil 35 a pipe 38 leads to supply pipe 39 connected to desuperheater 12 and through which the proper amount of refrigerant liquid is supplied from the condenser to maintain the pool of liquid in that vessel. A suitable expansion valve 40 in pipe 36 controlled in response to the temperature of the contents of pipe 38 as by means of thermostat 41, assures the proper cooling of the liquid in tank 33, and if non-condensible gas should become entrapped at the top of the suction tank 33 a suitable valve 42 in branch pipe 43 will vent such gas into line 38 and thence into the vessel 12.

Connected to the sub-cooled suction tank is a pump intake 44 from which pump 45 draws liquid refrigerant, without causing flashing of the contents of the suction tank, and supplies liquid at for example p.s.i.g. through pipe 46 into reservoir 47 associated with the vaporizer. From an upper portion of reservoir 47 a pipe 50 leads liquid to a second receiver 51 also equipped with improved means to avoid carry-over of oil which may settle in that receiver. Refrigerant liquid from this receiver, which represents the high pressure region or plant pressure of the system, is delivered by pipe 52 to a heat transfer coil 53 disposed in the pool of liquid in the desuperheater l2 and after passage through coil 53 this liquid, which then may be at about 50F. and at about 150 p.s.i.g. is delivered by pipe 54 through valve 57 to float communicating with and controlling liquid level in evaporator 56. In general, passage of this clean liquid through coil 53 serves to lower its tempera ture which thus reduces flash gas at the expansion or float valve 55. Spent gas from the evaporator enters pipe 10 controlled bya conventional dual pressure control valve 58 as for example a Type A4CB valve available from Refrigerating Specialties Co. of Broadview, 111., and thus returns to the booster compressor 11. The proper amount ofliquid in the pool in vessel 12 is maintained by a branch supply pipe 60 connected to pipe 84 and to supply pipe 61 which forms an extension of pipe 39. A control valve 62 in branch pipe 60 responsive to a thermostat 63 which senses the level of the pool liquid may be employed.

Reference now is made to H6. 2 showing an improved oil collecting trap serving as the main oil removal point of the system and by means of which oil can be automatically removed. This trap comprises an elongated tank 66 disposed beneath the desuperheater vessel 12 and connected thereto by pipe 67 extending to near the bottom of tank 66 and under control of a suitable valve 68. The tank contains apertured sloping baffles 69 and cold oil-contaminated refrigerant liquid enters the tank from the desuperheater with the oil collecting at the bottom of the tank and with liquid refrigerant thereabove and with some refrigerant gas above the liquid. A return pipe 70 controlled by a suitable flow regulating valve 71 permits return of the liquid and gas to the desuperheater 12 below the liquid level therein. From the bottom of the tank 66 an oil withdrawal pipe 72 controlled by an automatically operable valve 73 and by a normally open back up valve 74 is provided; An external pipe 75 having a thermostat 76 thereon, which senses the warmer oil in tank 66 and controls operation of valve 73, is connected by branch piping to pipe 72, to the lower portion of the tank, to the upper portion of the tank, and to pipe 70. Accordingly, when the warm oil in the trap rises to a prescribed level it is automatically expelled from the system throughpipe 72 and when the cold liquid falls to a prescribed level the valve 73 closes.

As will now be noted, with valves 68 and 71 opened to permit regulated flow, the agitated oil-laden liquid from the pool in desuperheater l2 and which has been cooled, due to flashing of liquid supplied from the condenser, enters the trap 66 continuously, due to density difference of the contents flowing in the respective legs 67 and 70 of the structure, deposits the heavier oil in the trap, and after passing the baffles 69 the lighter liquid returns through pipe 70. The small amount of gas which flashes from the cold liquid during travel through the trap also returns to the desuperheater through pipe 70.

While the above-described trap is particularly well suited to the improved refrigeration system of the present invention it may, of course, be employed with conventional refrigeration systems at points where cold oilladen refrigerant liquid is collected.

In the present system, oil-laden refrigerant gas arrives at desuperheater 12 from an improved desuperheater and oil removing unit 23 as best shown in FIG. 3. This unit comprises a vessel containing baffles 80 with a rough edge apertures in its exit section as disclosed in the aforementioned patent, and with an improved gas and liquid contact means in its entry section. Oilcontaining gas from compressor 20 after passing through a precooling stage in vaporizer 22 may still be at a temperature of about 200F. and a pressure of about 76 p.s.i.g. as it enters pipe 21. This pipe, which contains an elevated loop 81 above unit 23 to insure against reverse flow of liquid, enters one end of vessel 23 into an enlarged pipe bend 82 whose distal end is directed toward that one end of the vessel in the gas space of the same. An equalizing pipe 77 connects this gas space to the elevated loop and has a check valve 78 opening toward that loop. The lower portion ofthe pipe bend is cut away to permit liquid to stand at a desired level and significantly, a weir 83 is affixed to the interior of the pipe bend so that gas entering from pipe 21 must bubble beneath the liquid level at the weir in order to enter the vessel and in so doing the gas is cooled by the flashing ofa portion of the liquid. Further gas and liquid contact is provided by the spray of incoming liquid from a supply pipe 84 whose discharge end is perforated as at 85 and is disposed within the pipe bend. Pipe 84 connects with the outlet from the elevated condenser 26 to supply liquid refrigerant at condenser pressure and at an appropriate static head. Moreover, as seen in FIG. 4, valve 86 responsive to a float in tank 87 controls the liquid supply to the vessel 23. By means of branch pipes 88 89 connecting this tank to the respective gas and liquid spaces in the vessel 23 the level of liquid causing incoming gas to bubble under weir 83 can be maintained. As disclosed in said earlier patent, the oil in the gas entering from pipe 21 is transferred to the liquid in the vessel 23 as it is cooled by flashing of a portion of this liquid and while being mechanically obstructed by the baffles in its passage to outlet pipe 24. Upon entering that pipe it is directed as a clean gas to the condenser for conversion to a liquid or can be employed for defrosting of the evaporator.

A trap 90 disposed beneath vessel 23 receives liquid from that vessel through an open pipe 91 extending to near the bottom of the trap and has an open pipe 92 connecting the upper portion of the trap to the vessel. Leading from one end of the trap is pipe 36 in which the withdrawal of oil laden liquid is controlled by the aforementioned thermostatic valve 40 responsive to the temperature of the gas leaving coil 35 in suction tank 33. Normally, all of the oil separated in the vessel 23 passes through pipe 36 on its way to the desuperheater 12 for later automatic expulsion from the system, but if desired a draw off pipe 93 controlled by valve 94 may be employed with trap 90.

Reference now is made to FIGS. 1A and 5 showing the multipurpose vaporizer 22 in its relation to other elements of the system. This unit may comprise a closed tank 100 containing a body of vaporizable liquid, such as water, introduced into the tank at filling port 101. Heat insulation (not shown) is provided about the tank, and the pipe 21 carrying hot compressed gas from compressor to the desuperheater vessel 23 passes axially through the tank in heat transfer relation to the body of liquid at the lower part of the tank and to the body of steam at the upper part of the tank. Accordingly, the vaporizer serves as a precooler for gas travelling on to the condenser, and the body of liquid with its suitable latent heat of vaporization serves as a heat storage agent providing reliable pressurization of the second receiver 51 in the manner now to be described. The heat storage capability is such that rapid vaporization of liquid in the coil 102 will occur as pressure conditions change in the system.

This coil 102 surrounding pipe 21 within the tank is supplied with liquid refrigerant through pipe 103 under gravity flow from the lower end of reservoir 47. From the upper end of this coil pipe 104 leads refrigerant gas back to the upper end of the reservoir. This gas, which due to heat extraction from the body of liquid and steam in the tank has flashed from the liquid supplied through pipe 103, is at a pressure (for example, about 150 p.s.i.g.) corresponding to the high pressure point of the system. An open ended sleeve 105 mounted in tank 100 in surrounding relation to pipe 21 beneath the level of the liquid serves to aid in the heat transfer action by defining convection currents and if desired a separate heating element (not shown) may be employed to aid in heating the body of water in the tank rapidly at start-up.

Connected to pipe 104 is a vent pipe 106 extending to pipe 38 and controlled by valve 107 opening into pipe 38. Equalizing pipe 110 connects pipe 104 to the top of second receiver 51 and serves to establish the plant pressure therein resulting from vaporization of the liquid in coil 102. A pressure switch 111 which senses this plant pressure serves to control a valve 112 through which liquid is supplied to coil 102 for vaporization therein. A flow-regulating valve 113 in inlet pipe 103 also is employed to control liquid flow to the vaporizer coil. Preferably the liquid pump 45 is driven by a motor 115 and by means of a switch 116 responsive to a float within the second receiver the pump can be operated as needed to maintain the desired liquid level in receiver 51.

When condenser pressure approaches plant pressure and pump 45 is not being operated, flow of liquid from suction tank 33 to reservoir 47 takes place by means of pipe 117 connecting a lower portion of that reservoir to pipe 46. A check valve 118 in pipe 46 is adapted to close when pump 45 is inoperative and a check valve 119 in pipe 117 opens when the pump is being bypassed.

As will now be apparent, during normal operation of the system refrigerant liquid substantially free of oil is supplied through pipe 54 to the evaporator which, however, requires defrosting from time to time. A feature of the invention is that defrosting may be conducted with clean cooled refrigerant rather than with hot oilladen refrigerant. When defrosting, the dual pressure control valve 58 is closed and clean gas at a temperature of about 75F. and at a pressure of about 65 p.s.i.g. after passing through a pressure reducer 120 and an opened valve 121, enters the evaporator and condenses to a liquid with concomitant withdrawal of heat and defrosting, the valve 57, of course, being closed at this time.

The condensed liquid will remove any oil which may have been deposited earlier on the' inner surface of the evaporator and will pass through the open drain valve 122 into collecting tank 123 which in turn drains into pipe 39 which normally carries oil-laden refrigerant to desuperheater 12. A float within tank 123 controls operation of a valve 124 through which condensate is passed and a branch pipe 125 having a valve 126 therein serves as a means for venting refrigerant gas after the defrosting has been completed and valve 121 is closed. Following this venting, valve 122 is again closed and both the dual pressure control valve 58 and valve 57 are again restored to their normal operating settings.

Considering now FIGS. 6 to 9, the first and second receivers preferably are equipped with identical means for preventing oil-carryover from such receivers and for avoiding oil-foam generation in the receiver. Refrigerant condensate flowing through pipe 30 from the elevated condenser passes into the receiver 31 through the stem 130 of a T-shaped tube connected to pipe 30. This stern communicates with at least two branch portions 131 and 132 whose open ends are directed upwardly and terminate below the normal level of liquid maintained in the receiver, but substantially above the lowest portion of the receiver. Any oil which may have reached the receiver previously will (due to its difference in specific gravity) have settled to the bottom of the receiver and should it be agitated by incoming or outgoing liquid or gas from the receiver, an oil foam will result and which would be carried over from the receiver with either or both of gas and liquid. By distributing the liquid from pipe 30 in this manner the formation of foam can be largely prevented even when fluctuations of flow from the condenser are occuring. As a supplement to the described distributor for incoming liquid, the receiver is equipped with an open-top box like trap attached to the pipe 34 through which liquid is moved to the suction tank 33. This trap which is submerged in liquid comprises side walls 133 and 134 attached at their upper ends to pipe 34. A bottom 135 of the trap is disposed adjacent the bottom of the receiver and an upwardly directed open end wall 136 of the trap acts to keep oil from entering the trap as the oil level approaches the top of the box and as liquid is being withdrawn through pipe 34 at high velocity due to surge flow. Oil collected in the receiver and undisturbed by agitation may be withdrawn at any time through outlet 137 upon opening of a valve 138.

As a further aid in reducing power consumption of the system and preventing rapid pressure fluctuations and surge conditions which would mitigate against optimum removal of oil, the invention comprehends the control of condenser 26 in dependence upon the pressure of gas being supplied thereto for condensing. As is known, when a rapid pressure drop (which may be caused by change in weather conditions, decrease of load on evaporators, starting of pumps, or the like) occurs, boiling ofliquid in receiver 31 or in desuperheater 23, or in both, may occur and this will cause agitation of the liquid and of the oil which may have already settled out in those structures. This agitation results in the formation of gas bubbles having a film of oil and which (unless again broken up and separated) will allow carry-over of oil through the system.

Referring now to FIG. 1B condenser 26 may be supplied with cooling water from a reservoir 140 and moved by pump 141 through line 142 into contact with the condenser coils. Alternately, the condenser may be air cooled in which event a fan 141 would move compressed air through a duct 142 into contact with the coils. In either event the member 141 is driven by a motor 143 controlled by a combined pressure-and-time responsive switch 144. The pressure applied to such switch is the gas pressure in pipe 24 and the time factor applied to the switch is chosen as desired and is applied by means of an adjustable clock setting.

For example, a suitable setting may provide that the switch will open and stop the motor 143 whenever the pressure in pipe 24 falls at a rate greater than 5 p.s.i.g. per minute and will close and start the motor within 2 minutes whenever such pressure ceases to fall, and will close and start the motor at once when the pressure begins to rise.

Since the desuperheater 23, the first receiver 31, and the condenser 26 are all operating at approximately the same pressure, a rapid pressure drop in this section of the system, and which the described control will serve to prevent, would otherwise cause flashing and boiling of liquid, entrainment of oil, and deposit of such oil on heat transfer surfaces downstream from this section of the system.

In addition to the prevention of such boiling, the automatic switching of motor 143 permits operation of the condenser at uniform and economical minimum pressures thus leading to a substantial saving of power consumption.

As will be apparent to those skilled in the art the improved over-all system and the arrangement of the several elements of apparatus within the system takes advantage of the desuperating of gases and the subcooling of liquids through the flashing of liquid at condenser pressures, rather than at plant pressure which is more costly to obtain.

Having thus described and illustrated the preferred embodiments of the invention, it will be appreciated that the invention may, of course, be embodied in other forms within the scope of the appended claims.

What is claimed is:

l. A refrigeration system comprising in combination. a condenser, a first receiver connected to said condenser, a second receiver, means for moving liquid from said first to said second receiver, an evaporator supplied with liquid refrigerant from said second receiver, an oil-lubricated compressor receiving gas from said evaporator and for compressing the same with development of heat, a combined desuperheater and oilseparating unit receiving precooled contaminated gas from said compressor and supplying clean gas to said condenser, said unit having a conduit extending therefrom for removal of impurities separated therein from the gas, and a vaporizer receiving liquid refrigerant from said first receiver and returning gaseous refrigerant to said second receiver, said vaporizer serving simultaneously to precool the hot compressed gas leaving said compressor and to produce a cushion of clean high pressure gas above the liquid in said second receiver and having sufficient pressure to force refrigerant liquid to said evaporator.

2. A system as defined in claim 1 wherein said means for moving liquid from said first to said second receiver comprises a motor driven pump.

3. A system as defined in claim 2 wherein the operation of said pump is controlled in dependence upon the amount of liquid stored in said second receiver.

4. In a refrigeration system having first and second receivers and a pump for selective movement of liquid refrigerant from said first to said second receiver; the improvement comprising a suction tank at the intake of said pump, a pipe extending from said first receiver to the upper portion of said tank for filling of said tank with liquid, a pipe extending from said pump for movement of liquid to said second receiver, and a refrigerant coil disposed within said tank in heat exchange relation to the liquid to be pumped and serving to maintain the temperature of said liquid in the tank belowits boiling point.

5. Apparatus as defined in claim 4 including means for passing liquid from said suction tank to said second receiver without passing through said pump.

6. A refrigeration system comprising in combination, a condenser, a first receiver connected to said condenser, a second receiver, means for moving liquid from said first to said second receiver, an evaporator supplied with liquid refrigerant from said second receiver, an oil-lubricated booster compressor receiving gas from said evaporator and for compressing the same with development of heat, a first desuperheater receiving gas from said booster compressor, means for cooling said gas in said first desuperheater and for separating oil therefrom, means for removing the separated oil at the bottom of said first desuperheater, a main oillubricated compressor receiving gas from said first desuperheater and for compressing the same with development of heat, a combined desuperheater and oil separating unit receiving precooled contaminated gas from said main compressor and supplying clean gas to said condenser, said unit having a pipe extending therefrom for removal of the separated oil, and a vaporizer receiving liquid refrigerant from said first receiver and returning gaseous refrigerant to said second receiver, said vaporizer serving simultaniously to precool the hot compressed gas leaving said main compressor and to produce a cushion of clean high pressure gas above the liquid in said second receiver and having sufficient pressure to force refrigerant liquid to said evaporator.

7. A system as defined in claim 6 wherein said first desuperheater includes a supply conduit receiving liquid refrigerant from said condenser and in sufficient quantity to form a pool of liquid through which gas from said booster compressor is passed.

8. In a refrigeration system having an oil-lubricated compressor, a condenser and a receiver; the improvement comprising a combined desuperheating and oilseparating unit receiving hot gas from said compressor and passing oil-free cooled gas to said condenser, said unit including an elongated vessel having an inlet pipe connected at one end to said compressor and an outlet pipe at the other end connected to said condenser, an enlarged pipebend at said one end of said vessel having its discharge end directed toward said one end of said vessel, said pipe bend having a cut away portion into which liquid may enter to establish a liquid level'within said vessel, a depending weir mounted within said pipe bend and under which incoming gas from said compressor is compelled to pass and to mix with said liquid with a bubbling action, a stand pipe having spray openings adjacent its top and mounted in said vessel and extending into said pipe bend, means for supplying a regulated amount of liquid from said condenser to said stand pipe for cooling of said gas by flashing of a portion of the liquid supplied from said condenser, and a pressure equalizing pipe extending from said receiver and connected to the outlet pipe from said other end of said vessel whereby substantially the same pressure may be maintained in the gas spaces of said vessel, said condenser and said receiver.

9. Apparatus as defined in claim 8 including an oil trap connected to the bottom of said vessel and into which oil-containing liquid drains, and means for automatically removing the contents of said trap.

10. In a refrigeration system having an oil-lubricated compressor, a condenser, a first receiver, a second receiver and a combined desuperheating and oil removal unit; the improvement comprising a vaporizer having a tank containing a body of vaporizable liquid, a pipe for passing hot gas from said compressor through said tank in heat exchange with said liquid and for delivery of a precooled gas into said unit for cleaning of the gas therein, a pipe for passing cleansed refrigerant liquid from said condenser to said first receiver, means for transferring refrigerant liquid from said first receiver to said second receiver, a pipe coil in said tank in heat exchange with said body of vaporizable liquid, means for supplying to the lower portion of said coil a regulated amount of cleansed refrigerant liquid transferred from said first receiver and for conversion to relatively high pressure gas within said coil, and means for passing refrigerant gas from an upper portion of said coil into the gas space of said second receiver.

11. Apparatus as defined in claim 10 including an open end sleeve mounted in surrounding relation to said hot gas pipe within said tank and submerged in said body of vaporizable liquid thereby to enhance convection currents within the body of vaporizable liquid.

12. Apparatus as defined in claim 10 including means for regulating the amount of cleansed refrigerant liquid supplied to said coil for vaporization in dependence upon the pressure in the gas space of said second receiver.

13. Apparatus as defined in claim 10 wherein said body of vaporizable liquid comprises water and said tank includes a steam space above the level of the body of water with said coil being in heat exchange with both hot water and steam, said water and steam serving as a heat storage means.

14. In a refrigeration system having an oil-lubricated booster compressor, a desuperheater, a main compressor, a combined desuperheating and oil separating unit, a condenser, a receiver and an evaporator; the improvment comprising an oil-collecting trap from which oil may be removed during operation of the system, said trap including an elongated tank disposed beneath said desuperheater and receiving continuously therefrom a cold mixture of refrigerant liquid and oil; said mixture being cooled by flashing of refrigerant liquid passing from said condenser and said mixture including as constituents refrigerant gas together with oil coming from said compressor and which has been removed from said desuperheating and oil separating unit; said trap having an inlet pipe connected to the bottom of said desuperheater and return pipe extending from an upper portion of its tank to said desuperheater at a location above the bottom of said desuperheater and below the level of liquid in said desuperheater, an oil drain pipe extending downwardly from the bottom of the oil trap tank, and a normally closed valve in said drain pipe adapted when opened to permit venting of oil while circulation is being maintained between said trap and said desuperheater.

15. Apparatus as defined in claim 14 including inclined apertured baffle means within said elongated tank serving to rupture bubbles, collect oil and to establish a pool of heavier oil at the bottom of said tank and a bodyof lighter refrigerant liquid at the upper portion of said tank.

16. Apparatus as defined in claim 15 including a flow regulating valve in said return pipe and adapted to adjust the rate of circulation caused by density difference in liquid-oil mixture entering at bottom of said trap tank and liquid-gas mixture leaving at top of said tank.

17. Apparatus as defined in claim 14 wherein said drain pipe valve is automatically operated in dependence upon temperature differences caused by the rise and fall of the oil level within said trap.

18. In a refrigeration system having a condenser, 21 combined desuperheater and oil removing unit supplying gas through an outlet pipe to said condenser, and a receiver receiving liquid from said condenser and including a gas space connected by a pressure equalizing pipe to said outlet pipe from said unit; the improvement comprising, pumping means for the cooling medium supplied to said condenser, a motor for driving said pumping means, and a rate of change control switch for said motor responsive to the pressure existing in said outlet pipe and equalizing pipe, whereby as said pressure drops rapidly said switch will operate to open the motor circuit and when said pressure drop is arrested or said pressure starts to rise said switch will operate to close said motor circuit.

19. Apparatus as defined in claim 18 including means in said receiver for reducing foaming of oil and refrigerant, and means connected to said unit for removing oil separated in said unit and for preventing the carryover of the same through said system.

20. in a refrigeration system having a condenser, an evaporator, and a receiver having a first pipe receiving liquid from the condenser and a second pipe extending from the receiver for furnishing liquid to said evaporator; the improvement comprising means for reducing the foaming of oil and refrigerant in said receiver and the movement to said evaporator of oil collected below the liquid in said receiver and comprising, a distributor at the lower end of said first pipe adapted to introduce without substantial turbulence the liquid supplied into said receiver, and a trap at the inlet end of said second pipe and spaced above the bottom of said receiver whereby surges of liquid leaving said receiver through said second pipe will not disturb oil collected in said receiver below said trap.

21. Apparatus as defined in claim 20 wherein said distributor comprises a plurality of upwardly directed submerged outlets receiving liquid from said first pipe and discharging into said receiver above the oil collected therein.

22. in a refrigeration system having an oil-lubricated compressor, a condenser, an evaporator, a desuperheater, and a combined desuperheating and oil separating unit through which gas passes from said compressor to said condenser; the improvement comprising means for diverting a portion of the oil-free gas moving from said unit to said condenser and passing the diverted gas into said evaporator for defrosting the same, means for passing the liquid condensate formed from the gas employed for defrosting into said desuperheater, and means for passing gas from said desuperheater to said compressor and thence to said unit.

23. Apparatus as defined in claim 22 including means for passing a portion of said diverted portion of gas which isnot condensed in the defrosting of said evaporator into said desuperheater following the defrosting of said evaporator thereby to sweep any oil from said evaporator surfaces into said desuperheater. 

1. A refrigeration system comprising in combination, a condenser, a first receiver connected to said condenser, a second receiver, means for moving liquid from said first to said second receiver, an evaporator supplied with liquid refrigerant from said second receiver, an oil-lubricated compressor receiving gas from said evaporator and for compressing the same with development of heat, a combined desuperheater and oil-separating unit receiving precooled contaminated gas from said compressor and supplying clean gas to said condenser, said unit having a conduit extending therefrom for removal of impurities separated therein from the gas, and a vaporizer receiving liquid refrigerant from said first receiver and returning gaseous refrigerant to said second receiver, said vaporizer serving simultaneously to precool the hot compressed gas leaving said compressor and to produce a cushion of clean high pressure gas above the liquid in said second receiver and having sufficient pressure to force refrigerant liquid to said evaporator.
 2. A system as defined in claim 1 wherein said means for moving liquid from said first to said seCond receiver comprises a motor driven pump.
 3. A system as defined in claim 2 wherein the operation of said pump is controlled in dependence upon the amount of liquid stored in said second receiver.
 4. In a refrigeration system having first and second receivers and a pump for selective movement of liquid refrigerant from said first to said second receiver; the improvement comprising a suction tank at the intake of said pump, a pipe extending from said first receiver to the upper portion of said tank for filling of said tank with liquid, a pipe extending from said pump for movement of liquid to said second receiver, and a refrigerant coil disposed within said tank in heat exchange relation to the liquid to be pumped and serving to maintain the temperature of said liquid in the tank below its boiling point.
 5. Apparatus as defined in claim 4 including means for passing liquid from said suction tank to said second receiver without passing through said pump.
 6. A refrigeration system comprising in combination, a condenser, a first receiver connected to said condenser, a second receiver, means for moving liquid from said first to said second receiver, an evaporator supplied with liquid refrigerant from said second receiver, an oil-lubricated booster compressor receiving gas from said evaporator and for compressing the same with development of heat, a first desuperheater receiving gas from said booster compressor, means for cooling said gas in said first desuperheater and for separating oil therefrom, means for removing the separated oil at the bottom of said first desuperheater, a main oil-lubricated compressor receiving gas from said first desuperheater and for compressing the same with development of heat, a combined desuperheater and oil separating unit receiving precooled contaminated gas from said main compressor and supplying clean gas to said condenser, said unit having a pipe extending therefrom for removal of the separated oil, and a vaporizer receiving liquid refrigerant from said first receiver and returning gaseous refrigerant to said second receiver, said vaporizer serving simultaniously to precool the hot compressed gas leaving said main compressor and to produce a cushion of clean high pressure gas above the liquid in said second receiver and having sufficient pressure to force refrigerant liquid to said evaporator.
 7. A system as defined in claim 6 wherein said first desuperheater includes a supply conduit receiving liquid refrigerant from said condenser and in sufficient quantity to form a pool of liquid through which gas from said booster compressor is passed.
 8. In a refrigeration system having an oil-lubricated compressor, a condenser and a receiver; the improvement comprising a combined desuperheating and oil-separating unit receiving hot gas from said compressor and passing oil-free cooled gas to said condenser, said unit including an elongated vessel having an inlet pipe connected at one end to said compressor and an outlet pipe at the other end connected to said condenser, an enlarged pipebend at said one end of said vessel having its discharge end directed toward said one end of said vessel, said pipe bend having a cut away portion into which liquid may enter to establish a liquid level within said vessel, a depending weir mounted within said pipe bend and under which incoming gas from said compressor is compelled to pass and to mix with said liquid with a bubbling action, a stand pipe having spray openings adjacent its top and mounted in said vessel and extending into said pipe bend, means for supplying a regulated amount of liquid from said condenser to said stand pipe for cooling of said gas by flashing of a portion of the liquid supplied from said condenser, and a pressure equalizing pipe extending from said receiver and connected to the outlet pipe from said other end of said vessel whereby substantially the same pressure may be maintained in the gas spaces of said vessel, said condenser and said receiver.
 9. Apparatus as defined in clAim 8 including an oil trap connected to the bottom of said vessel and into which oil-containing liquid drains, and means for automatically removing the contents of said trap.
 10. In a refrigeration system having an oil-lubricated compressor, a condenser, a first receiver, a second receiver and a combined desuperheating and oil removal unit; the improvement comprising a vaporizer having a tank containing a body of vaporizable liquid, a pipe for passing hot gas from said compressor through said tank in heat exchange with said liquid and for delivery of a precooled gas into said unit for cleaning of the gas therein, a pipe for passing cleansed refrigerant liquid from said condenser to said first receiver, means for transferring refrigerant liquid from said first receiver to said second receiver, a pipe coil in said tank in heat exchange with said body of vaporizable liquid, means for supplying to the lower portion of said coil a regulated amount of cleansed refrigerant liquid transferred from said first receiver and for conversion to relatively high pressure gas within said coil, and means for passing refrigerant gas from an upper portion of said coil into the gas space of said second receiver.
 11. Apparatus as defined in claim 10 including an open end sleeve mounted in surrounding relation to said hot gas pipe within said tank and submerged in said body of vaporizable liquid thereby to enhance convection currents within the body of vaporizable liquid.
 12. Apparatus as defined in claim 10 including means for regulating the amount of cleansed refrigerant liquid supplied to said coil for vaporization in dependence upon the pressure in the gas space of said second receiver.
 13. Apparatus as defined in claim 10 wherein said body of vaporizable liquid comprises water and said tank includes a steam space above the level of the body of water with said coil being in heat exchange with both hot water and steam, said water and steam serving as a heat storage means.
 14. In a refrigeration system having an oil-lubricated booster compressor, a desuperheater, a main compressor, a combined desuperheating and oil separating unit, a condenser, a receiver and an evaporator; the improvment comprising an oil-collecting trap from which oil may be removed during operation of the system, said trap including an elongated tank disposed beneath said desuperheater and receiving continuously therefrom a cold mixture of refrigerant liquid and oil; said mixture being cooled by flashing of refrigerant liquid passing from said condenser and said mixture including as constituents refrigerant gas together with oil coming from said compressor and which has been removed from said desuperheating and oil separating unit; said trap having an inlet pipe connected to the bottom of said desuperheater and return pipe extending from an upper portion of its tank to said desuperheater at a location above the bottom of said desuperheater and below the level of liquid in said desuperheater, an oil drain pipe extending downwardly from the bottom of the oil trap tank, and a normally closed valve in said drain pipe adapted when opened to permit venting of oil while circulation is being maintained between said trap and said desuperheater.
 15. Apparatus as defined in claim 14 including inclined apertured baffle means within said elongated tank serving to rupture bubbles, collect oil and to establish a pool of heavier oil at the bottom of said tank and a body of lighter refrigerant liquid at the upper portion of said tank.
 16. Apparatus as defined in claim 15 including a flow regulating valve in said return pipe and adapted to adjust the rate of circulation caused by density difference in liquid-oil mixture entering at bottom of said trap tank and liquid-gas mixture leaving at top of said tank.
 17. Apparatus as defined in claim 14 wherein said drain pipe valve is automatically operated in dependence upon temperature differences caused by the rise and fall of the oil level within said trap.
 18. In a refrIgeration system having a condenser, a combined desuperheater and oil removing unit supplying gas through an outlet pipe to said condenser, and a receiver receiving liquid from said condenser and including a gas space connected by a pressure equalizing pipe to said outlet pipe from said unit; the improvement comprising, pumping means for the cooling medium supplied to said condenser, a motor for driving said pumping means, and a rate of change control switch for said motor responsive to the pressure existing in said outlet pipe and equalizing pipe, whereby as said pressure drops rapidly said switch will operate to open the motor circuit and when said pressure drop is arrested or said pressure starts to rise said switch will operate to close said motor circuit.
 19. Apparatus as defined in claim 18 including means in said receiver for reducing foaming of oil and refrigerant, and means connected to said unit for removing oil separated in said unit and for preventing the carryover of the same through said system.
 20. In a refrigeration system having a condenser, an evaporator, and a receiver having a first pipe receiving liquid from the condenser and a second pipe extending from the receiver for furnishing liquid to said evaporator; the improvement comprising means for reducing the foaming of oil and refrigerant in said receiver and the movement to said evaporator of oil collected below the liquid in said receiver and comprising, a distributor at the lower end of said first pipe adapted to introduce without substantial turbulence the liquid supplied into said receiver, and a trap at the inlet end of said second pipe and spaced above the bottom of said receiver whereby surges of liquid leaving said receiver through said second pipe will not disturb oil collected in said receiver below said trap.
 21. Apparatus as defined in claim 20 wherein said distributor comprises a plurality of upwardly directed submerged outlets receiving liquid from said first pipe and discharging into said receiver above the oil collected therein.
 22. In a refrigeration system having an oil-lubricated compressor, a condenser, an evaporator, a desuperheater, and a combined desuperheating and oil separating unit through which gas passes from said compressor to said condenser; the improvement comprising means for diverting a portion of the oil-free gas moving from said unit to said condenser and passing the diverted gas into said evaporator for defrosting the same, means for passing the liquid condensate formed from the gas employed for defrosting into said desuperheater, and means for passing gas from said desuperheater to said compressor and thence to said unit.
 23. Apparatus as defined in claim 22 including means for passing a portion of said diverted portion of gas which is not condensed in the defrosting of said evaporator into said desuperheater following the defrosting of said evaporator thereby to sweep any oil from said evaporator surfaces into said desuperheater. 